Multiple vent



Dec. 26, 1961 w. J. STEWART 3, 4,

MULTIPLE VENT Filed April 15. 1959 2 Sheets-Sheet 1 FlG.-2

William J. Stewart IIVVEIVTOR A TTORIVE Y Dec. 26, 1961 Filed April 13, 1959 W. J. STEWART MULTIPLE VENT 2 Sheets-Sheet 2 FlG.-4

William .1. Stewart lA/VENTOR By 7 WATTORNBIY'Y 3,014,615 MULTIPLE VENT William .l. Stewart, Fair-haven, Ni, assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Apr. 13, 1959, Ser. No. 805,905 4 Claims. (till. 2 2il85) The present invention is concerned with an improved apparatus and method for venting storage tanks, particularly underground motor fuel and related products stor age tanks. The apparatus of the present invention comprises a unique type of safety header or manifold into which a plurality of tank vent lines are connected in a particular manner. A vent line extending from the header is then utilized.

It is well known in the art, particularly, in the sale of motor fuels and the like, to position a plurality of storage tanks containing various grades of motor fuel and other related hydrocarbon products underground at the service stations. These tanks vary appreciably in type of design and size. For example, the capacities of these tanks may be in the range from. about 550 gallons to about 4,000 gallons. The sizes may vary from about 4 feet in diameter to 6 feet long, to about feet, 4 inches in diameter to 24 feet long. in general, these tanks are placed beneath the surface at a distance of at least 3 feet which is required by underwriters, or may be placed at a greater depth.

Each tank has a fill line which extends from the surface to within the tank to a point from about 10 inches to 14 inches, usually about 12 inches above the bottom of the tank. about 2 to 4 inches. Furthermore, each tank has a vent line, 1 to 2 inches in diameter, extending from the top of the tank. This vent line normally comprises a short vertical section, a relatively long substantially horizontal section which is positioned underground and extends to a point removed from the tank, and a riser section. In design, it is preferred that the substantially horizontal section pitch upwardly from the tank to the riser section. in most instances, the riser section is positioned behind the building. Thus, when the tank is filled with liquid as, for example, with gasoline through the fill line, gasoline vapors in the tank are expelled through the vent line and are discharged to the atmosphere at an elevated point, generally behind the building. This technique widely distributes the vapors and minimizes hazards of fire and explosion due to the presence of anexplosive mixture of air and gasoline vapors.

While in general, the procedure has been entirely satisfactory, in many instances due to settling of the earth, changes in grade and the like, the vent line does not pitch upwardly from the tank, thus permitting backfiow of liquid into the tank. The result is that under certain conditions, the vent line entraps a certain amount of. rhotor fuel. This is particularly the case when the loader .fills the tank over and above capacity, which forces fuel into the vent line. Thereafter, when the tank is emptied due to sale of the motor fuel, the entrapped liquid does The diameter of the fill line may vary from p not flow back into the tank but remains in the horizonv tal section of the vent line.

When refilling tanks at service stations and the like to avoid undue interference with business conditions and saleof product at the service stations. Thus,,if this desire is to be secured and if there should be entrapped liquid in the vent line, the rapid filling of the tank with liquid results in a precipitous surge of expelled vapor through the vent line, which in turn, forcibly ejects the slug of entrapped liquid motor fuel from the vent line into the surrounding atmosphere. This slug forms a fine liquid spray which distributes itself over a very wide area. The spray contacts buildings, personnel, clothing and causes damage. In addition, this fine spray of volatile liquid mixed with air represents a distinct hazard with respect to tire, explosion and health.

Heretofore, when this condition existed, it was necessary to carry out expensive excavating and correct the condition. However, in accordance with the present invention, this condition is effectively and efiiciently corrected by the utilization of a unique type of safety header into which a plurality of vents from at least several tanks are connected.

The apparatus and process of the present invention may be readily understood by reference to the drawings illustrating embodiments of the same. FIG. 1 shows two tanks positioned below ground and the respective connecting lines, while FIG. 2 shows in some detail the manifold and manner of connecting the respective lines. FIG. 3 shows one specific embodiment of the safety header of the present invention and FIG. 4 shows an. end view thereof.

Referring specifically to FIG. 1, tanks 1 and 2 are shown positioned below the surface 3. These tanks, for the purpose of description, are cylindrical drums in design and have capacities in the range from about 550 to 4,500 gallons. A fill line 4- enables liquid to be introduced into tank 1 from the surface, while a fill line 5 enables tank 2 to be filled with liquid from the surface. A vent line 6 extends from the top of tank 1 to a riser 7 which extends above building 8. A vent line 9 extends from the top of tank 2 to a riser 10 which extends above building 8. These risers '7 and 10 are connected to manifold 11 containing a vent 14 positioned at one end thereof. Manifold 11 also contains risers l2 and 13 which, in turn, may be connected to other subterranean tanks. Tanks 1 and 2 are connected by a yoke line 15. Under certain conditions, vent lines s and 9 pitch downwardly from the respective tanks to the risers. Thus, volatile liquid will be entrapped in these lines and will be forcibly ejected as a fine spray into the atmosphere around the area of building 3, causing damageand creating a hazard as hereinbefore described. As pointed out heretofore, liquid is usually forced into vent line 6 when tank 1. is filled to over-capacity through fill line 4. This is not prevented in operation even thougha certain amount of liquid can flow into tank 2 through yoke line 15. Generally, yoke line 15 is about 2 inches in diameter. operation, the tanks on the tanktruck are from 7 to 10 feet above the ground and thus the liquid head into the tank may be as much as 12 to 20 feet. The liquid thus surges intotank l at a very rapid rate so that when tank lis filled, the yoke line cannot handle the over-flow resulting in liquid flowing into line 6. The same situation to any appreciableextent during filling of any one tank which otherwise might be the case since, as pointed out heretofore, the liquid head from the tank on the tank truck to ground level may be as much as 10 feet. Risers '7 and 10 are shown connected to the bottom of the manifold 11 along with additional risers 12 and 13 which connect to two additional tanks not shown in a manner similar to the manner connecting risers 7 and 1b to tanks 1 and 2. A single 3-inch vent 14- positioned at one end of manifold 11 extends from the top of the manifold. The length is at least 5 feet and should not exceed about feet.

While the manifold and method of connecting the line may be varied somewhat, the following is a typical satisfactory arrangement. The risers extending from tanks 1 and 2 have diameters of about 3 inches. These risers '7, 10, 12 and 13 are manifolded at the bottom of manifold 11 at or approaching one end thereof.- The riser 14 is positioned at the opposite end thereof extending from the top of 11. This vent L;- should have a diameter of about 3 inches and have a length of about 5 feet. Thus the top of this vent will be at least 13 feet above grade.

With respect to the manifold itself, the dimension may likewise vary. However, it is preferred to have an overall length of about 18 to 36 inches, preferably, about 24 inches. The back side thereof should be flat and have a height of about 4 to 10 inches. Six inches is preferred. A portion of the top and bottom should be also flat and comprise parallel planes, the width of which is about 4 to 10 inches. The front of the manifold preferably comprises a structure semi-cylindrical in design extending the entire length of the unit. in general, the radius of the cylinder should be about 2 to 6 inches. A 3-inch radius is preferred.

Thus, in operation, if one or more of the vent lines contain volatile liquids when the tank corresponding to that particular vent line is rapidly filled with additional liquid, rapidly expelling vapors, the vapors will eject the slugs of liquid fuel into the manifold to which the vent is attached. This manifold will effectively and efilciently remove the liquid from the vapors, permitting the liquid to flow into another vent line and drained back into another tank. Meanwhile, the vapors free of entrained liquid, pass upwardly from the manifold and are discharged into the atmosphere.

FIGS. 3 and 4 illustrate one specific satisfactory design of the safety manifold of the present invention. The dimensions are as follows:

In order to further illustrate the invention, the following tests were conducted.

Example A number of tanks were tested to determine certain characteristics of high velocity venting of underground storage tanks. In order that the entire process of venting from the tank to the riser could be studied visually, a 2 inch clear plastic vent line was installed. All field conditions otherwise were simulated.

A 6,100 gallon capacity truck without meters was used with a standard 12 x 4" hose and tight fill (Evertite) connections. Air temperature at beginning of tests was 58 F. and the temperature of product in the truck was 62 F.

The first run was made from a 510 galloncompartment with all conditions normal to establish a control delivery rate. This was determined to be 273 g.p.m.

Subsequent runs were made as follows:

' (l) Tank-was allowed to overfill under normal conditions with product .yoking over and filling vent risen (2) Tank'emptied and again filled under normal delivery conditions.

(3) Tank emptied, then overfilled With-liquid trapped in vent, diameter 1%" in l0.' run. g

(4) Tank emptied, then filled withproduct trapped in portion of vent. This particular test-was repeated several times with varying amounts of trap.

(5) Tank allowed to overfill to obtain yoke flow-over rate.

(6) Delivery made through valved fill line to determine maximum fiow rate without blow-out.

The findings were as follows:

(A) When the yoked tanks are overfilled with a tight fill connection, the product is forced up into the vents to a point approximately equal to the product level in the truck. Under normal conditions, this product drains rapidly back into the tank when delivery is completed. Subsequent deliveries are then made without incident.

(B) However, where there is a trap in the horizontal vent run, the produc. remains in line indefinitely. Due

to the vacuum set up in the tank due to yoking over or use of island pump, the product is pulled out of vent pipe until sulficient area is available for normal displacement venting, i.e., the air entering the tank. For this reason the depth of the trap is of no particular importance. All

other conditions being the same, a slight trap (V2 inch or under) may be just as bad as a severe trap of 2 inches or more.

(C) A tight fill, non-metered delivery to a tank the has been previously overfilled and has a trapped vent, will inevitably result in a blow-out. The degree of severity of this condition depends on the length of the run rather than the depth of trap, and delivery rate.

(D) Under maximum head conditions, the best delivery rate that could be obtained through a 2 inch bar yoke was g.p.m. This represents a decrease of nearly of the normal delivery rate. In other words, it will take nearly 2 minutes longer to yoke over 1,600 gallons than it will to disconnect and make a straight delivery.

(E) A rate of delivery was also determined at which blow-out occurs. It appears that regardless of the depth of trap, delivery in excess of 209 gpm. will cause trouble and at 200 g.p.m. and under, no blow-out should be expected.

The present invention is concerned with an improved safety manifold which insures that no liquid spray from underground storage tanks will be passed into the atmosphere endangering property and health. Furthermore, the present invention permits the rapid filling of underground tanks in a minimum of time from tank trucks.

What is claimed is:

1. Improved apparatus for the storage of combustible liquids which comprises a plurality of subterranean storage vessels, a vent line from each of said vessels, said vent lines comprising underground substantially horizontal runner sections extending away from said vessels, substantially vertical riser sections attached to each of said runner sections at a point distant from said vessels, a manifold section positioned above the surface of the earth attached to the upper end of said riser sections in a manner that the ends of said riser sections are flush with the bottom of said manifold so as to permit drainage, and a second atmospheric vent line extending vertical from said manifold.

2. Apparatus as defined in claim 1 wherein said manifold section is attached to said risers at a point at least 10 feet above the surface of the earth,

3. Apparatus as defined in claim 1 wherein said manifold section is characterized by a rectangular fiat back, a rectangular flat top in parallel relationship with a rectangular fiat bottom and a front semi-cylindrical in form.

4. Improved apparatus for the storage of combustible liquids which comprise a plurality of subterranean storage vessels, a vent line from each of said vessels, said vent lines comprising substantially horizontal runner sections extending away from said vessels, substantially vertical riser sections attached to each of said runner sections at a point distant from said vessels, a manifold section attached to the upper end of said riser sections and a second atmospheric vent line extending from said manifold, said manifold'section being characterized by a rectangular flat back, a rectangular flat top in parallel relationship with a rectangular flat bottom and a front semicylindrical in form, said apparatus being further characterized in that said riser sections are attached to the bottom fiat surface of said manifold adjacent one end thereof and said atmospheric vent line being attached to the top flat surface of said manifold section adjacent the other end thereof.

References fiited in the file of this patent UNITED STATES PATENTS Appleman Dec. 18, 1928 Schlicht Apr. 13, 1937 Koch Feb. 1, 1938 Marner Nov. 17, 1942 

